Drive line slip joint assembly

ABSTRACT

A drive line joint assembly (10) has splined driving and driven members (13,20), one of which has a protuberance (36) which extends axially along a spline (16,18) thereof to insure the absence of radial tolerance for balancing purpose. In a preferred form, a forged steel spline (16) has a resilient coating (40) bonded thereto, the coating preferably of a nylon or of other material having comparable low friction quality. The resilient protuberance is an integral part of the latter low friction coating and is formed by a broaching tool after the coating material has been applied to the spline. In a preferred embodiment, the proturberance extends only 0.001 to 0.003 inch above the surface of the coating, wherein the coating has a thickness in the range of 0.007 to 0.014 inch over the steel body portion of the spline. At least three of the protuberances are preferred, each circumferentially spaced from the other. The protuberances are utilized to take up all radial slack between driving and driven members of the drive line joint assembly, thereby allowing for no radial movement of one member with respect to the other.

BACKGROUND OF THE INVENTION

This invention relates to slip joint assemblies as utilized in drivelines. More particularly, the invention relates to an apparatus andmethod for reducing radial slack due to tolerances between rotarydriving and driven splined members.

Many prior art devices have been employed to aid the reduction of slackbetween splined rotary members. For example, U.S. Pat. No. 3,318,170discloses a system of balls, springs and collars for minimizing orreducing lateral movements between annular members. U.S. Pat. No.1,438,935 discloses a system of spaced projections 22 which reduceradial movement between annular rotary members. U.S. Pat. No. 3,383,882,on the other hand, discloses a system of fingers in a pair of splinedconcentric members, wherein the fingers operate to radially secure aninner member 15 relative to an outer member 14.

Although each of these devices performs in a satisfactory manner, thedevices are cumbersome and expensive to manufacture, and are notparticularly suitable in those instances where one of the concentricsplined driving and driven members is coated with a bonded low-frictionmaterial. In the latter circumstances, the manufacture of theafore-noted devices would involve special considerations to insureprotection of the coatings.

SUMMARY OF THE INVENTION

The invention disclosed herein provides a system whereby the radialtolerances between driving and driven splined members may be absorbedwithout the use of complex apparatus or equipment and/or cumbersomemanufacturing techniques. The apparatus and method herein disclosed areparticularly suitable for situations wherein at least one of either thedriving or driven members includes a low-friction coating bondedthereto.

In a preferred embodiment, the apparatus includes an axially extendingresilient protuberance along at least three splines circumferentiallyspaced about one of the members. Each of the splines includes a coatingof a material having a low-friction characteristic, and the protuberanceextends in the range of 0.001 to 0.003 inch above the surface of thecoating. The protuberance is preferably an integral part of the coatingmaterial. In a preferred method, the spline is coated with thelow-friction material, and then broached to remove a thin layer of thematerial and to produce an axially extending protuberance over the facesof the three circumferentially spaced splines of one of the members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial view partly in cross section of a stub shaft andspline sleeve in driving relationship, wherein the stub shaftincorporates the present invention;

FIG. 2 is a view in elevation of the stub shaft of FIG. 1;

FIG. 3 is a view along lines 3--3 of FIG. 1; and

FIG. 4 is a fragmentary cross sectional view of one full spline of thestub shaft which incorporates the present invention, taken along lines4--4 of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A drive line slip joint assembly 10 which incorporates the presentinvention is shown in FIG. 1. The slip joint assembly 10 includes a stubshaft or driving member 12 having a splined, enlarged portion 14 moreclearly shown in FIG. 2. The enlarged portion 14 contains radiallyoutwardly extending splines 16 which engage radially inwardly extendingsplines 18 of a mating sleeve 19 of a driven member 20. The drivenmember 20 in turn includes an integral yoke 22 for transmission of driveline torque.

Referring momentarily to FIG. 4, each outwardly extending spline 16defines a pair of side walls 24, which inwardly terminate into aU-shaped bottom groove 26. The groove 26 provides means for receivingthe mating splines 18 (FIG. 1) on the sleeve 19, and also provides forpassage of lubricant. Conventional means are employed to manufacture thespline and groove shapes as discussed herein, typically by hobbing. Adirt seal 28 (FIG. 1) protects the rightward end of the assembly 10against the intrusion of dirt or other contaminants, and also providesfor prevention of lubricant escape. The rightward end of the stub shaft12 further contains an integral extension 30 which is affixed to motivemeans (not shown).

Referring now to FIGS. 3 and 4, it will be seen that the radiallyoutwardly extending walls 24 of the splines 16 terminate at relativelyflat axially extending faces 32, which cooperate with but are spacedfrom corresponding flat faces 34 within the mating sleeve 19. It will benoted that the flat faces 32 of spline 16 are positioned at the terminalportions of the radially outwardly extending walls 24, while the flatfaces 34 of the mating sleeve 19 are positioned between the individualsplines 18 thereon. Thus, it will be appreciated that the flat faces 34of the mating sleeve circumscribe an imaginary circle 33 which forms theoutermost peripheral portion of a bore 35 through the driven member 20.Similarly, it will be seen and appreciated that the flat faces 32 of themating splines 16 circumscribe an imaginary circle 31 which forms theoutermost peripheral portion of the driving member or stub shaft 12.Concentric circles 31 and 33 are for convenience represented by a singledotted circle in FIG. 3. To the extent that there is a small amount ofclearance between the mating driving and driven members (generally 1-2thousandths of an inch), there will be a difference between thediameters of the respective circles; specifically, the outer circle 33will be larger than the inner circle 31. The disparity in diameters,preferably in the range of 0.0015 to 0.0020 inch, will in fact create apotential balancing problem at particularly high speeds of operation.For example, a 250 ounce drive shaft which is free to move radially0.0020 inch will generate an unbalance of potentially one-halfinch-ounce. The unbalance becomes more critical as the speed of thedrive shaft increases, due to the fact that balancing forces increase asa square of rotational speeds.

In the embodiment of FIGS. 3 and 4, the mating faces 32 and 34 arepositioned at the outermost peripheral portions of the members 12 and20, respectively, as described. Alternatively, the groove 26 could beadapted into a circumferentially extending face disposed for mating withthe innermost peripheral face 40 of the splines 18 of the member 20(FIG. 3). The latter situation is also within the scope of the presentinvention.

The invention as herein defined thus provides an axially extending,resilient protuberance 36 on a circumferentially spaced plurality offaces 32 on splines 16. (Alternatively the faces between the splines 18may contain circumferentially spaced protuberances.) The protuberancesare virtually microscopic in size, each having a radially extendingdimension of only 0.001 to 0.003 inch. They resiliently operate to takeup any radial slack or looseness (also referred to as "play") due toaccumulation of tolerances between driving and driven members 12 and 20for dynamic balancing purposes. The protuberances preferably aretriangular in cross section, and have a dimension of approximately 0.009to 0.012 inch at the base thereof, which forms is greatest dimension aswell as its attachment to an individual spline. Each protuberance has awidth less than the circumferential width of the face to which it isattached. In the preferred embodiment the face width is in the range of0.040 to 0.125 inch.

In the preferred form of this invention, the protuberance 36 is a partof an applied coating 38, preferably one having a nylon base, as fullydescribed in U.S. Pat. No. Re. 27,068. The latter coating comprises ahardened adhesively bonded low-friction material which provides forimproved relative movement between splined driving and driven members.The preferred thickness of the nylon coating as applied over thepreferably forged steel driving member 12 is constant to within lessthan one thousandth of an inch variation, and is in a preferred range of0.007 to 0.012 inch.

A preferred method of making the protuberance includes the steps ofadhesively applying the resilient nylon coating 38 to the splinedportion of the member 12, and then removing a portion of the coatingafter application of the nylon to form the projection 36. A preferredmethod of removal is by a broaching operation wherein a single pass ismade over the splined external portion of the member 12. For thispurpose, particularly with use of hardened nylon material, a carbidering is a preferred broaching apparatus.

Thus, for example, a commercially available nylon powder sold under thetrademark "Corvel" NCA-77 nylon may be applied to a heat treated forgedsteel stub shaft 12 as described in U.S. Pat. No. Re. 27,068. However,instead of machining the coating to final tolerances as describedtherein by grinding, the outer peripheral faces or spline faces 32 arecut to final size in a single-pass broaching operation, wherein thecutting edges are notched. The cutting edges preferably have V-shapednotches, to leave a triangular shaped protuberance on at least threecircumferentially spaced spline faces 32 about the splined portion 14 ofthe stub shaft driving member 12. A standard vertical broaching fixturemay be employed, wherein the shaft 12 is held rigidly upright on centers(bored into the ends of the shaft), and wherein the broaching toolpasses downwardly over the splines via hydraulic pressure actuation.

As mentioned, each protuberance 36 is preferably triangular in crosssection, having its widest dimension at the base of the triangle, whichforms its attachment to an individual spline. The triangular shape ofthe protuberance, and particularly the wide base thereof, maximizeslateral stability and strength and yet provides greatest resilience atthe outer extremity of the protuberance where most needed. The preferredradially extending dimension (or height) of the triangle is 0.001 to0.003 inch, the latter range in correspondence with the aforementioneddisparity in diameters of inner and outer circles 31,33 (of 0.0015 to0.0020 inch). It will be readily apparent to those skilled in the artthat greater disparity in diameters will require greater dimensions ofthe protuberances for effective results. In any case, to the extent thatthe plurality of radially extending protuberances must resiliently, butpositively, take up all slack between driving and driven members, theprotuberances must extend physically a slight amount beyond the outercircle 33. Moreover, they must be elastically flexible for assuring atight but resilient, slidable mating contact between driving and drivenmembers for satisfactory operation.

What is claimed is:
 1. A drive line slip joint component having aplurality of axially extending splines, each spline comprising anaxially extending face, each face having a circumferentially extendingwidth, at least two of said faces each comprising one resilient axiallyextending protuberance, each of said faces further comprising alow-friction coating bonded thereto, each resilient protuberancecomprising an integral portion of said coating, said coating generallyhaving a constant thickness over said face, said thickness within therange of 0.007 to 0.014 inch, and said protuberance extending 0.001 to0.003 inch above the surface of said coating said protuberances beingcircumferentially spaced apart about said component, said protuberancesproviding means for enhancing the dynamic balancing of said component.2. The slip joint component of claim 1 wherein said low-friction coatingcomprises a nylon base.
 3. In a drive line slip joint assemblycomprising a driving and a driven member, said driving membertelescopically engaging a bore through one end of said driven member,said members respectively having intermeshing externally and internallysplined portions forming a driving connection therebetween, saidexternally splined portion of said driving member defining a pluralityof radially outwardly extending splines, each spline having a pair ofside walls extending axially over said driving member, said splineshaving axially extending faces generally perpendicular to said sidewalls, said internally splined portion of said driven member defining aplurality of radially inwardly extending splines, each spline having apair of side walls extending axially over said member each side wall ofsaid driven member being disposed for cooperative contact with one ofsaid side walls of said driving member, said splines of said drivenmember having axially extending faces wherein said faces of said drivingmember are spaced from said faces of said driven member; an improvementcomprising at least two of said axially extending faces on one of saiddriving and driven members having an axially extending, resilientprotuberance thereon, each of said faces further comprising alow-friction coating bonded thereto, each resilient protuberancecomprising an integral portion of said coating, said coating generallyhaving a constant thickness over said face, said thickness within therange of 0.007 to 0.014 inch, and said protuberance extending 0.001 to0.003 inch above the surface of said coating said protuberances beingcircumferentially spaced apart about said one of said driving and drivenmembers, said protuberances being elastically flexible for insuringslidable mating contact between driving and driven members, saidprotuberances providing means for enhancing the dynamic balancing ofsaid assembly.
 4. The slip joint assembly of claim 3, wherein saidoutermost peripheral portions of said bore of said driven member andsaid outermost peripheral portions of said driving member lie onconcentric outer and inner circles respectively, the outer circlecircumscribing the outermost peripheral portions of said bore and havinga diameter in the range of 0.0015 to 0.0020 inch greater than that ofsaid inner circle. .Iadd.
 5. A drive line slip joint component having aplurality of axially extending splines, each spline comprising anaxially extending face, each face having a circumferentially extendingwidth, at least two of said faces each comprising one resilientprotuberance, each of said faces further comprising a low-frictioncoating bonded thereto, each resilient protuberance comprising anintegral portion of said coating, said coating generally having aconstant thickness over said face, said thickness within the range of0.007 to 0.014 inch, and said protuberance extending 0.001 to 0.003 inchabove the surface of said coating, said protuberances beingcircumferentially spaced apart about said component, said protuberancesproviding means for enhancing the dynamic balancing of said component..Iaddend. .Iadd.6. The drive line component of claim 5 wherein at leasttwo of said protuberances are parallel with respect to one another.